Various methods are known for inducing sleep and include frequency following response (FFR) techniques and the use of binaural tones. In addition, methods are known in which a person can train himself/herself to replicate a desired state of consciousness without the need for audio stimulation. U.S. Pat. No. 5,213,562 discloses such a method and the ability to transfer such states from one individual to another by inducement of a binaural beat phenomenon. This is achieved by using electroencephalography (EEG) signals from one individual superimposed on stereo signals that are applied to another individual.
U.S. Pat. No. 5,356,368 discloses a method that uses FFR to facilitate attainment of desired states of consciousness. Sleep patterns are reproduced based on observed brain patterns during portions of a sleep cycle.
U.S. Pat. No. 4,573,449 discloses a method and apparatus in which sound pulses are emitted by an electro-acoustic transducer to assist a person suffering from sleeplessness to become relaxed and fall asleep. An individual using the device is required to breathe in and out over a predetermined period of time in accordance with the cadence of the pulses. Selection of the pulse sequence frequency, pitch and amplitude of the sound pulses are adjustable to enhance the process of falling asleep.
In U.S. Pat. No. 3,753,433, the use of audio tones and a binaural headset is disclosed. The headset is worn by a user and includes scalp electrodes that are placed on the head of the user when the headset is worn. The electrodes pick up brain wave signals which are converted to recognisable audio tones for the user so that the user can listen to his/her own brain waves.
WO-A-2006/101571 discloses a method that uses binaural beat for balancing the brain left side with the brain right side. An EEG system is used to measure the electrical signals produced by each side of the brain and an audio generator is used to generate the binaural beat to compensate for the imbalance.
In WO-A-00/16842, a digital sound relaxation system is disclosed in which sounds are used to mask ambient sounds and to induce a state of deep relaxation that helps the listener to fall asleep. Different modes are selectable by selecting a combination of mode select and sequential sound selector switches. An alarm mode is included that allows one or more sounds from a pre-recorded library to be used as the wake-up sound.
US-A-2009/105524 discloses a device for inducing sleep by playing music having a tempo of between sixty and eighty beats per minute to provide better sleep quality, better perceived sleep quality, longer sleep duration and greater sleep efficiency. The device may be provided in an alarm clock, a pillow, mobile, sleep mask, crib or a stuffed toy for use with children. The sleep-inducing device can also be made transportable for inducing better sleep during travel.
U.S. Pat. No. 3,884,218 discloses a method for inducing sleep in which familiar repetitive pleasing sounds are used, in combination with EEG signals, to induce various stages of sleep. The pleasing sounds are modulated by the EEG sleep signals. The pleasing sounds change in amplitude and frequency in accordance with the modulation of the EEG sleep signals. The audio signal is played continuously until a predetermined wake-up time in which they will stop allowing the individual to drift back to wakefulness.
By modulating the pleasing sounds with EEG sleep signals, they change in amplitude and frequency, and, such changes can disturb a user's sleep, particularly if large amplitude and frequency changes are experienced.
U.S. Pat. No. 5,135,468 discloses a method and apparatus for varying the brain state of a person in which first and second audio signals at respective first and second frequencies are provided to respective ears, the first and second audio frequencies varying in a range of approximately 0 to 60 Hz. In addition, the amplitude of each audio signal is varied so that the person perceives a constantly moving sound. Three embodiments are described in which a person can be relaxed, sent to sleep or energised in accordance with the type of binaural beat bands utilised.
WO-A-95/17854 discloses a trophotropic response system which aids a user in achieving a relaxation response. The system comprises a control unit and an audiovisual unit. The control unit includes a processor and associated hardware and software to control the audiovisual unit which comprises a light producing unit and a pair of headphones coupled thereto. Light from the light producing unit is directed onto a diffuser screen located between the eyes of a user and light sources located within the light producing unit. In this way, both light and sound are produced in response to control signals provided by the control unit to aid the user in performing a relaxation exercise. However, it would be impractical to use such a system as a sleep aid.
US-A-2008/0304691 discloses a sleep aid system in which speakers are enclosed in fabric to provide soft comfortable headphones that can be work as a sweatband or a watch cap when worn by a user. Binaural beat technology may be used where binaural beats are provided to the user via the sleep aid system. Alarm or wake-up functions may also be provided. However, a user of the system described in US-A-2008//0304691, needs to wear headphones when sleeping to be able to benefit from the use of the sleep aid.
WO-A-2008/131454 describes a sleep inducing and maintenance system in which binaural beat frequencies are used, the system comprising a soft fabric sleep mask into which are incorporated light-emitting diode (LED) elements and speakers. Coloured LED elements are matched to each binaural beat frequency and operate in synchronism with the binaural beat frequency. A binaural voice object is used to produce a binaural beat which plays a single part in a four part song, each part corresponding to one of alpha, beta, delta and theta brainwaves. Song files are disclosed which comprise a list of variable-length records ordered by time which are repeated until the particular session ends. Session files are used to adjust the intensity of the binaural beats with respect to time. A push button is used to index through sequences that relate to “go to sleep”, “go back to sleep”, “wake up” and “meditate”, and another push button is used to start the chosen sequence.
It is therefore an object of the present invention to provide a device which promotes healthy, natural sleep patterns using binaural beat frequencies combined with either a background environmental sound which does not suffer from the problem of changes in amplitude and frequency of the environmental sound or a subliminal tone at a frequency that is not discernible to the user in the case where the user prefers a quiet room when sleeping.